Children born to fathers 40 and older have nearly six times the risk of autism as those born to dads 30 or younger. Researchers from the Mount Sinai School of Medicine in New York and King's College in London examined data on more than 300,000 individuals to reach this conclusion, which was published in a recent issue of the Archives of General Psychiatry.

Autism, a disorder involving social, language and behavior problems, now afflicts about 5.5 out of every 1,000 children. And while older parental age has been linked with other developmental problems, this is one of the first studies to examine its impact on autism. The study did not find a link between maternal age and autism.

The researchers theorize that mutations in sperm-producing cells or alterations in gene "imprinting" as men age could be behind increased autism risk.

"Although further work is necessary to confirm this interpretation," the authors note in their report, they believe that the study "provides the first convincing evidence that advanced paternal age is a risk factor for autism spectrum disorder."